I have recently used the Synology update to update the Mylar app on the Diskstation.
Now finally updates worked by clicking on "update" in the popup.
Befor that I had to update manually with sudo git pull.

They Syno stuff is tied to the master branch, so that's what it's updating against. Your mylar is set to look against the development branch - thus the discrepancy.

The commit you mention is actually the master branch.

With mylar shutdown, edit the config.ini and find the git_branch value. If it's set to development, set it to master. If it's set to master, set it to development. Then save the config.ini and start mylar up. You shouldn't see the update message any longer.

When I switch to Master it goes away - and when I switch back to development it is back again.
I have been on the development branch for years and would prefer to stay on that.
Is there anything else I can do?

That should put you on the development branch and then perform an update against the dev branch too (if it's needed). Just make sure you config.ini git_branch value is on development and you should be good to go from that point forward (updates might be different as it might still be tied to the SynoPkg Master installation - I haven't a clue in that particular regards unfortunately).

Otherwise, you'd possibly have to do away with the SynoPkg install and just use a straight git clone if you'd want to remain on the development branch without any further problems (this is me just best guessing here, I really don't have any idea about how the SynoPkg stuff works, I just know that it's always been tied to the Master branch).

So I guess this did not work.
I'll look into doing the git clone thing.

Thank you for the help

Well all that means is that you're up-to-date on the development branch according to git. However if you're using the SynoPkg stuff, again it's tied to the Master branch. Because your config.ini is set to development, and now your git is set to development, you should be on the development branch and Mylar would be checking against said branch when querying updates.

When you start up Mylar, does it still indicate that you're not up-to-date or that you're behind in commits? If it does, what does the branch indicate that you're on (both at the bottom the page, and on the 1st tab of the configuration GUI) ?